ref: move TestHub to SentryTestUtils

[armcknight]

Need this to be able to write a new profiler test in #3938 that needs a hub instance, and I don't want to use the live hub.

Had to rewrite testSpanFinishesAfterTracerReleased_NoCrash_TracerIsNil in swift, added to SentryTracerTests.swift, for the same reason as in #3968, I can't figure out how to import SentryTests-Swift.h into objc test classes.

#skip-changelog

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 90.881%. Comparing base (297f460) to head (b55e1e8).

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3986       +/-   ##
=============================================
+ Coverage   90.867%   90.881%   +0.014%     
=============================================
  Files          594       593        -1     
  Lines        46351     46347        -4     
  Branches     16598     16601        +3     
=============================================
+ Hits         42118     42121        +3     
+ Misses        4163      4156        -7     
  Partials        70        70               

Files	Coverage Δ
...ts/SentryTests/Transaction/SentryTracerTests.swift	98.364% <100.000%> (+0.025%)	⬆️
SentryTestUtils/TestHub.swift	60.869% <60.869%> (ø)

... and 6 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 297f460...b55e1e8. Read the comment docs.

[philipphofmann]

LGTM, thanks 👍